This invention relates generally to the field of fluid-solid contacting. More specifically, this invention deals with the delivery of fluids to beds of particulate material.
Fluid-solid contacting devices have a wide variety of applications. Such devices find common application in processes for hydrocarbon conversion and adsorption columns for separation of fluid components. When the fluid-solid contacting device is an adsorption column, the particulate material will comprise an adsorbent through which the fluid passes. In the case of hydrocarbon conversion, the fluid-solid contacting apparatus is typically a reactor containing catalyst. Typical hydrocarbon conversion reactions that may be carried out are hydrogenation, hydrotreating, hydrocracking, and hydrodealkylation.
Fluid-solid contacting devices to which this invention apply are arranged as an elongated cylinder usually having a vertical orientation through which an essentially vertical flow of fluid is maintained. Particulate material contained in this vessel is arranged in one or more beds. Fluid enters the vessel through an inlet located at an upstream end of the vessel. It is also commonly known to add or withdraw fluid from between the particulate beds. This is commonly done in adsorption schemes where the composition of the fluid passing between particle beds is changing or in hydrocarbon conversion processes where a quench system is used to cool fluid as it passes between beds.
Many of the feeds to such processing units may contain debris. Such debris can consist of small solid particulate material flowing in liquid or gas streams, or discrete droplets of heavy viscous material flowing in either liquid or gas streams. Feeds containing such material are usually referred to as dirty and include single phase or multiphase streams. Such feed components may be part of the feed itself or may be the result of corrosion or deterioration of upstream processing equipment. Typically, the concentration of such material in any feedstream is not high, but over time it can disrupt the operation of the fluid contacting bed. Particulate material can accumulate over the top of the bed surface thereby raising the pressure drop through the bed, or heavy viscous debris can form gummy surfaces that will eventually plug the top surface of the bed.
A common design approach for treating dirty feeds is to provide debris catchers along the surface of the particulate bed. These debris catchers are typically in the form of extended cylinders or baskets that have an open top and extend into the bed anywhere from 1 to 2 or more feet. The gas stream to be contacted flows past the top surface of the bed into the top of the basket and radially outward through perforated sides of the basket. A substantial portion of the debris that enters the basket accumulates on the bottom of the basket.
While the basket design will prevent plugging of the top surface of the bed by debris, they do pose a number of drawbacks. First the presence of the basket affects the flow distribution through the bed. The baskets can cause a substantial portion of the flow through the processing vessel to bypass the upper surface of the bed. In addition, flow through the bed can disrupt the flow of fluid for several feet below the baskets. In addition, the baskets complicate loading of catalyst into the beds since they must be placed into the bed during the particle loading procedure.